In a photographic film thrusting cartridge system wherein photographic film wound on a spool within the cartridge may have an outer end that is thrust outward by reverse rotation of the spool, it is necessary or at least desirable, that the fully wound film roll maintain a predetermined minimum distance between the outer diameter of the film roll at its outer end and the adjacent inner wall of the cartridge. In order to accomplish this where a common size cartridge is used to contain filmstrips of varying sizes such as 12 exposure, 24 exposure, and 40 exposure lengths, it is possible to compensate for the varying filmstrip sizes by varying the core diameter of the associated film spool. Thus a 12 exposure filmstrip might be wound on a 12 mm spool core while a 40 exposure strip would require a spool core of only 7 mm diameter.
A problem with this proposal is that three different spool diameters are required to accommodate the three common variations of filmstrip length. This problem extends not only to the initial manufacture of film cartridges but also to so called "trouble roll" cartridges required by film processors for use as replacement cartridges in cases where a film cartridge provided by the customer is found to be defective. The differing spool core diameters used for the different filmstrips would require that the film processors have cartridges with all three spool sizes in stock for use with trouble rolls and this would increase the cost of manufacturing and storing the spare cartridges required.